1. Field of the Invention
The present invention relates to balloon angioplasty catheters and particularly to catheters which provide an inflation tube and a guidewire for pushability and steerability purposes.
2. Description of the Prior Art
There currently are two basic types of balloon angioplasty catheters--"over the wire" ("OTW") and "fixed wire" ("FW").
An OTW catheter provides a tube to accept a guidewire which is moveable and removable and can be extended distal to the distal end of the catheter for steering purposes. An inflation tube is also provided. The advantages of such a catheter are its steerability, column strength (pushability) and the possibility of exchange using the wire. The disadvantage is primarily the catheter's large profile since the device requires two tubes, one concentrically positioned inside the other, to provide an annular passage therebetween for passage of inflation fluid. The wire in such a catheter passes within the inner tube. Unfortunately, the number of components and the annular space increases the overall diameter (profile) of the device and limits its utility.
FW catheters have a single inflation tube around a fixed wire which allows a lower profile. However, this feature is gained at the expense of steerability, pushability and the ability to exchange the wire. Although FW catheters require only one tube and can therefore be smaller in cross-sectional diameter than an OTW catheter, the FW catheter requires space between the inside of the tube and the outside of the fixed wire for the passage of inflation fluid. The larger the diameter of the wire, the larger the diameter of the catheter --thereby limiting the utility of the catheter and also affecting its tractability. FW catheters are also limited because the physical characteristics of the wire, i.e., flexibility, diameter, and taper must be predetermined, thus compromising the FW device's ability to either cross a lesion or to steer the wire with a floppy tip that may be attached to the catheter. In such a situation, the FW catheter must be removed and replaced by another FW catheter, thereby causing further trauma to the blood vessel. These limitations were recognized in U.S. Pat. No. 4,932,959 to Horzewski et al. wherein a catheter is provided with a central tube which slidably receives a guidewire which can be moved back and forth to vary the flexibility of the distal end of the catheter. Unfortunately, in such a device the guidewire is a permanent part of the catheter, and a passage between the wire and the tube must be provided, thereby increasing the overall diameter of the catheter.
As seen from the above discussion, it would be desirable to have a balloon angioplasty catheter having a smaller overall diameter than an FW catheter, yet retaining the variable pushability and steerability of an OTW catheter.